Austenitic series stainless steel and relevant casting method

ABSTRACT

An austenitic series stainless steel and relevant casting method mainly comprises procedures of a preparation, a heat, a refinement, and a formation; wherein the present method mainly applies cheap scraps of stainless steels with about 13 to 18 wt % chromium basic to the manufacture. Further, the element manganese is used to substitute nickel and thence the proportion of nitrogen is increased while manufacturing. Accordingly, a component of the austenitic stainless steel of the present invention contains less than 0.08 wt % carbon, less than 0.9 wt % silicon, about 13 to 19 wt % manganese, less than 0.04 wt % phosphorus, less than 0.04 wt % sulfur, about 13 to 18 wt % chromium, less than 0.1 wt % nickel, less than 0.8 wt % nitrogen, and essentially iron and residuals. Such inclusion assists the austenitic stainless steel to attain same properties of preferable corrosion resistance and mechanism behaviors as those of the typical 300 series stainless steel.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a stainless steel, in particular to an austenitic stainless steel and its relevant casting method.

2. Description of the Related Art

Stainless steels are widely applied as their properties of favorable corrosion protection and easy fabrication, particularly to the more applications of an austenitic 300 series stainless steel on the general mechanical groceries in the daily life. Therefore, the manufactures of those steels would become the critical factors to affect their mechanical behaviors, for instance of points of tensile strength, yield strength, elongation, etc. in question.

As referring to FIG. 1 shows the component of an austenitic 304 stainless steel in which comprises the proportion in weight (wt %): 0.07 wt % carbon (C), 0.046 wt % silicon (Si), 1.44 wt % manganese (Mn), 0.025 wt % phosphorus (P), 0.03 wt % sulfur (S), 8.14 wt % nickel (Ni), 18.43 wt % chromium (Cr), 0.2 wt % nitrogen (N), and essentially iron (Fe) and other residuals. However, such typical composition possessing the at least 8.14 wt % nickel to reinforce the stability and the corrosion resistance of the stainless steel would certainly raise high material costs in virtue of the abounding demands exceeding the supply of the nickel. The nickel in short supply commonly requires a high price, which would probably become a weakness in the market.

Furthermore, the method 1 of manufacturing the conventional austenitic 304 stainless steel as depicted in FIG. 2, mainly comprises the incessant procedures of a preparation 11, a heating 12, a refinement 13, and a formation 14. Wherein, the preparation 11 is for initially preparing raw materials in response to the finished composition of the integral stainless steel, for example to use expansive and different minerals of elements or to use the popular adoption of scraps as the raw materials from the austenitic 304 stainless steel which provide similar characteristics for decreasing the costs. The heating 12 is to heat and melt the scraps within a closed vacuum furnace 121 so as to fuse them into liquid steel. Further, the refinement 13 serves to eliminate wastes from the liquid steel and attains pure liquid steel. The formation 14 thence processes the mold injection to pour the pure steel into a mold and solidifies it to produce an integral austenitic 304 stainless steel. From above, such typical method inevitably requires the raw materials comprised of the 8.14 wt % nickel in the preparing step and needs to replenish the insufficient nickel in the heating step. Nevertheless, the high expense of purchasing the nickel and large manufacture costs would make the burdens and thus require improvements.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an austenitic stainless steel and its relevant casting method which facilitates to decrease costs of the production by recycling scraps of stainless steels and to achieve the preferable corrosion resistance and the mechanism behaviors as the same as those typical 300 series stainless steel while applying a composition without a high proportion of the nickel.

The austenitic series stainless steel preferably comprises an anticipated composition in weight (wt %): less than 0.08 wt % carbon, less than 0.9 wt % silicon, about 13 to 19 wt % manganese, less than 0.04 wt % phosphorus, less than 0.04 wt % sulfur, about 13 to 18 wt % chromium, less than 0.1 wt % nickel, less than 0.8 wt % nitrogen, and balance essentially iron and other residual parts.

The method of casting the aforementioned austenitic stainless steel mainly includes the steps of a preparation for preparing basic scraps with 13 to 18 wt % chromium and mixing them into an admixture, a heating for placing the admixture into a high-frequency furnace 321 and fusing it into liquid steel, a refinement for purifying the liquid steel and replenishing insufficient parts of an actual component as to the expected component, and a formation for solidifying the pure liquid steel to create an integral austenitic stainless steel. Wherein, in the heating process, the addition of manganese replaces the nickel and the reinforcement of the nitrogen maintain the property of the corrosion resistance of the liquid steel and relieve the magnetic character thereof. Therefore, the present invention facilitates to achieve the preferable corrosion resistance and the mechanism behaviors without the application of a high proportion of the nickel.

The advantages of the present invention over the known prior arts will become more apparent to those of ordinary skilled in the art by reading the following descriptions with the relating drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a table showing a component of a conventional austenitic 304 stainless steel;

FIG. 2 is a brief diagram showing a method for manufacturing the conventional stainless steel;

FIG. 3 is a table showing a component of an austenitic series stainless steel of the present invention;

FIG. 4 is a schematic diagram showing a method of casting the austenitic stainless steel of the present invention;

FIG. 5 is a picture showing the organization of the present casted austenitic stainless steel under the 50× optical microscope;

FIG. 6 is a picture showing the organization of the present casted austenitic stainless steel under the 100× optical microscope;

FIG. 7 is another picture showing the organization of the present casted austenitic stainless steel under the 100× optical microscope;

FIG. 8 is a picture showing the organization of the present casted austenitic stainless steel under the 200× optical microscope;

FIG. 9 is a picture showing the organization of the present casted austenitic stainless steel under the 500× optical microscope;

FIG. 10 is another picture showing the organization of the present casted austenitic stainless steel under the 500× optical microscope; and

FIG. 11 is another picture showing the organization of the present casted austenitic stainless steel under the 500× optical microscope.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 3 showing a casting austenitic series stainless steel, of which an anticipated composition in weight (wt %) comprises:

a) less than 0.08 wt % carbon (C);

b) less than 0.9 wt % silicon (Si);

c) about 13 wt % to about 19 wt % manganese (Mn);

d) less than 0.04 wt % phosphorus (P);

e) less than 0.04 wt % sulfur (S);

f) about 13 wt % to about 18 wt % chromium (Cr);

g) less than 0.1 wt % nickel (Ni);

h) less than 0.8 wt % nitrogen (N); and

i) balance essentially iron (Fe) and other residual elements.

Additionally, with respect to attaining the development of the above anticipated composition, a method of manufacturing the aforementioned austenitic stainless steel includes the procedures set forth in FIG. 4: a preparation 31, a heating 32, a refinement 33, and a formation 34. Wherein, the present method has the preparation 31 provide scraps of stainless steels that provides with the inclusion of about 13 to 18 wt % chromium (Cr) as a foundation and merge them into an admixture in a particular proportions. It is not restricted sorts of the stainless-steel scraps and herein the 400 series stainless steel may be probably adopted as long as the 400 series scraps contains enough chromium. Furthermore, the application of the 400 stainless steel not only attains the economic benefit as it is cheaper than the 300 series stainless steel but renders the present method to have wide options in this preparing step 31.

Still further, in the heating step 32, a cheaper and open high-frequency furnace 321 substitutes for the typical and expensive closed vacuum furnace 121 as depicted in the prior art to far more decrease the expenses on the equipment. The admixture is placed and heated inside the high-frequency furnace 321, whose temperature is approximately between 1650 degree C. and 1750 degree C., and is fused into liquid steel; thereafter, the nitrogen and manganese are respective appended to ensure the liquid steel with less than 0.8 wt % nitrogen and about 13 to 19 wt % manganese therein, which hence could discretely maintain the corrosion resistance and release the magnetic property existing in the liquid steel. Herein, the additions of the chromium and the nickel are omitted to more save the costs as the liquid steel made by the scraps already possesses these two specific elements adapted to the appropriate quantity.

The refinement 33 is to remove impurities to refine the liquid steel into pure liquid steel, so that the present method could process to sample and take an examination on the pure liquid steel to acknowledge an actual a component thereof. The actual component with its interior proportions is compared with those of the anticipated component set forth above, and insufficient parts would be detected. Subsequently, a replenishment with those insufficient parts may be proceeded to render the actual composition able to conform to the scope of the anticipated component. The formation 34 infuses the pure liquid steel consisted of the anticipated component into a mold, then coagulates the pure liquid steel into a solid stainless steel, and thence releases the solid stainless steel from the mold. An integral formation of the austenitic stainless steel hence is finished.

Specimens of the above casted austenitic stainless steel were machined for a metallographic test as shown in pictures from FIG. 5 to FIG. 11. From the above experimental pictures, it plainly depicts the performances of the perlite and the austenitic steel for providing the considerable property of corrosion resistance and distinguishes from those of the austenitic stainless steel made by the typical method. Therefore, the present austenitic stainless steel in the anticipated composition set forth above accompanying with the relevant casting method facilitates to efficiently decrease the costs without more additions of the nickel and attain the preferable corrosion resistance and the mechanism behaviors.

To sum up, the present invention takes advantage of the manufacturing method to generate an austenitic stainless steel that possesses an actual composition adapted within the scope of an anticipated composition and to substitute other elements for the expensive nickel. Therefore, the present invention conduces to achieve lower manufacturing costs and assists the produced austenitic stainless steel to attain same properties of preferable corrosion resistance and mechanism behaviors as those of the typical 300 series stainless steel.

While we have shown and described the embodiment in accordance with the present invention, it should be clear to those skilled in the art that further embodiments may be made without departing from the scope of the present invention. 

1. A casting austenitic series stainless steel, having a composition in weight (wt %) comprising: a) less than 0.08 wt % carbon (C); b) less than 0.9 wt % silicon (Si); c) about 13 wt % to about 19 wt % manganese (Mn); d) less than 0.04 wt % phosphorus (P); e) less than 0.04 wt % sulfur (S); f) about 13 wt % to about 18 wt % chromium (Cr); g) less than 0.1 wt % nickel (Ni); h) less than 0.8 wt % nitrogen (N); and i) balance essentially iron (Fe) and other residual elements.
 2. A method of manufacturing a casting austenitic stainless steel, comprising steps of: a) preparing scraps of stainless steels, with the inclusion of chromium (Cr) from about 13 wt % to 18 wt %, wherein, said scraps being mixed with each other to become an admixture; b) placing and heating said admixture inside an open high-frequency furnace and fusing said admixture into liquid steel; appending elements of nitrogen (N) and manganese (Mn) into said liquid steel to contain less than 0.8 wt % nitrogen (N) therein for maintaining a corrosion resistance thereof, and to include about 13 wt % to 19 wt % manganese (Mn) therein for obviating magnetic properties thereof; c) removing impurities to refine said liquid steel into pure liquid steel; sampling and analyzing said pure liquid steel to prove actual rates among a component of said pure liquid steel, and comparing said actual component with said anticipated component claimed in claim 1 to add insufficient parts of said actual component in proportion to said anticipated component; and d) infusing said pure liquid steel consisted of said anticipated component into a mold and coagulating said pure liquid steel into a solid stainless steel; releasing said solid stainless steel from said mold and thus accomplishing a formation of said austenitic series stainless steel.
 3. The method as claimed in claim 2, wherein said high-frequency furnace has a temperature at the range preferably from 1650 degree C. to 1750 degree C. 